U.S. Pat. No. 4,395,109 describes a roller fusing mechanism for fusing toner to paper or another substrate in which a thin resistive heating layer is positioned close to the surface of a heated roller. This structure permits rapid and efficient transfer of heat to the surface of the roller. Consequently the surface temperature of the roller can be controlled more accurately, and less power is required to heat the roller surface.
This prior roller includes a core constructed of a metal, ceramic, or other material, onto which heat insulating and electrical insulating layers are applied. The electrical insulating layer acts as the support layer for the resistive heating layer. After the resistive heating layer is applied to the electrical insulating layer it is coated with an outer protective layer. This layer provides the fusing surface. Electrical contact between the resistive heating layer and power source is established by conductive rings and electrical brushes located at each end of the roller. Heating of the roller is established by continued current flow.
Rapid and efficient heat transfer to the fusing surface of the roller can be achieved by this structure, but its complex design requires many interfaces between layers. If the outer protective layer is made of a material requiring high temperature heat curing, for example, a fluorinated hydrocarbon, the high temperatures necessary for this process may cause separation at one of the layer interfaces, thus damaging the fusing roller.